The present invention relates to a registration system and to a method for phasing simultaneously advancing webs of materials, carrying pre-fabricated elements consecutively spaced at pitch lengths having small but significant variation, to a target web. Further, the present invention relates to consumer products, such as disposable absorbent articles, that may include an element or a registration mark which was included in the continuous webs before phasing with the target web in the process of making disposable absorbent articles by utilizing the instant registration system.
In the manufacture of disposable absorbent articles such as diapers and catamenials, it is a common manufacturing practice to combine continuously moving webs. These webs are typically represented by plastic films, non-wovens, elastics, etc. supplied to a converting line in their original production form and do not require special positioning before combining with other materials. However, the manufacture of disposable absorbent articles may benefit if the above materials are supplied to the converting line as prefabricated materials, i.e., produced off the converting line and carrying various elements of disposable absorbent articles consecutively spaced along the web length at a nominal pitch length determined by the length of a particular absorbent article. Because the pitch length between the consecutively spaced elements of the prefabricated materials can vary at small but significant variations, in order to ensure consistent positioning of the product elements in every absorbent article, there is a demand for a method to phase or register the consecutively spaced prefabricated elements to desired positions on a target web before combining the prefabricated materials with the target web into a final article or product.
The pre-fabricated elements may include preprinted registered graphic designs or characters that are desirably used in connection with disposable articles such as diapers to enhance their outward appearance for greater consumer acceptance. The positioning of a web preprinted with registered graphics such that the graphics are properly placed in relation to the rest of the diaper product is desirable, e.g., in order to provide a large-sized graphic without cutting it at an incorrect location, has been typically problematic. This is important not only for desirable aesthetic appearance, but also for example, because young children may become disturbed at seeing graphic representations of animals cut up into pieces (e.g., a head cut off).
In addition, breathable polymer films that are particularly useful as backsheet materials for disposable absorbent articles typically have good surface characteristics that make them suitable for the application of multi-colored, high resolution graphics, but such films tend to be mechanically unstable with a particular tendency toward thermal shrinkage in the machine direction. Such instabilities contribute to the difficulty in correctly positioning the pre-printed polymer web on the product web such that the graphic is correctly positioned, or phased, to the product web.
Various methods and apparatus have previously been used for combining such components in a desired relationship. For example, in conventional xe2x80x9cdiscrete phasingxe2x80x9d operations, the product is built around the printed graphic, by adjusting the timing position of the machinery in response to a correction signal. However, it cannot be used in operations where more than one web bearing a preprinted (or other phased object) is required for the process, since the machinery can move in response to the graphics on one web only. See, e.g., International Publication No. WO 96/29966.
In xe2x80x9cnon-continuous web placementxe2x80x9d operations, the graphic-printed web is discretized, or cut, into segments. Each segment is then placed on the target web or product in the desired position. This does not, however, ensure the centering of the graphic on the target web; furthermore, it limits the overall product design. The length of the discretized segments must be less than the length of the product, which may allow is leakage in the areas where the product is longer than the discretized segment, for example, in the waist region of a diaper.
Other control systems and apparatus for registration have been described, see International Publications WO 97/24094 and WO 97/24283. However, none of the existing systems or apparatus for registration addresses a system in which inherent significant material instabilities exist, nor do they address a system in which the pitch length of the preprinted graphic is non-uniform, particularly if the preprinted pitch length is longer than the pitch length of the product under production. Similarly, a control system such as that disclosed in U.S. Pat. No. 5,766,389 requires a fixed target pitch. In practice, the target pitch can be subject to the same instabilities as that of the registered printing.
Based on the foregoing, there is a need for a registration system for phasing simultaneously advancing webs having variable pitch lengths, at least one of which has consecutively spaced prefabricated objects (e.g., registered graphics), and the other of which (e.g., a diaper product web) contains consecutively spaced target objects (e.g., absorbent cores). Furthermore, there is a need for a registration control system that can account for the material specific instabilities that inherently exist in such webs and that present small but significant variations resulting therefrom, which make it difficult to combine such webs. In addition, there is a need for a system in which registration of incoming webs having either longer or shorter pitch lengths than the pitch length of the product under production is possible. None of the existing systems provides all of the advantages and benefits of the present invention.
The present invention is directed to a registration system for phasing simultaneously advancing webs of material having variable pitch lengths comprising: (a) means for feeding a continuous target web containing consecutively spaced target objects along a path at a first velocity, the target web having a target web pitch length between consecutive target objects; (b) means for feeding a continuous controlled web of material preprinted with consecutively spaced preprinted objects along a path at a second velocity, the preprinted web having a controlled web pitch length between consecutive preprinted objects; (c) means for adjusting the controlled web pitch length such that the controlled web pitch length is approximately equal to the target web pitch length; (d) detection means for detecting the preprinted objects of the controlled web; (e) means for generating an error signal based upon the detection of the preprinted objects of the controlled web; and (f) means for adjusting the second velocity such that the preprinted objects are shifted toward the target objects on the target web.
These and other features, aspects, and advantages of the invention will become evident to those skilled in the art from a reading of the present disclosure.